Structure and Oxidation State of Silica-Supported Manganese Oxide Catalysts and Reactivity for Acetone Oxidation with Ozone

Reed, Corey; Lee, Yong‐Kul; Oyama, S. Ted

doi:10.1021/jp054288w

Cited by 111 publications

(63 citation statements)

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“…Although numerous studies were conducted on the catalytic ozonation of VOCs [16][17][18][19][20][21][22][23], the underlying mechanism and its relevant kinetic steps remain unclear [24]. Other than the recent study by Rezaei and Soltan [24], no studies were performed to test the validity of the L-H s mechanism on the catalytic ozonation of toluene over alumina-supported manganese oxide catalysts.…”

Section: Introductionmentioning

confidence: 99%

Novel mechanistic view of catalytic ozonation of gaseous toluene by dual-site kinetic modelling

Yao

Hui

et al. 2017

Chemical Engineering Journal

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This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. AbstractThe catalytic ozonation of VOCs is a promising approach for degradation of indoor VOCs, such as gaseous toluene. However, the mechanism and relevant kinetic steps involved in this reaction remain unclear. In this study, the catalytic ozonation of toluene over MnO 2 /graphene was investigated using the empirical power law model and classic Langmuir-Hinshelwood single-site (denoted as L-H s ) mechanism. The apparent activation energy determined using the power law model was 29.3±2.5 kJ mol −1 . This finding indicated that the catalytic ozonation of toluene over MnO 2 /graphene was a heterogeneous reaction, and the Langmuir-Hinshelwood mechanism was applicable. However, the L-H s mechanism did not fit the experimental data, suggesting that the reaction was non-single-site governed. A novel Langmuir-Hinshelwood dual-site (denoted as L-H d ) mechanism was then proposed to explain the experimental observations of the catalytic ozonation of toluene over MnO 2 /graphene through a steady-state kinetic study. This mechanism was based on the hypothesis that MnO 2 was responsible for ozone decomposition and toluene adsorption on graphene; these two types of adsorption were coupled by an adjacent attack. Furthermore, XPS results confirmed the presence of a strong connection between MnO 2 and graphene sites on the surface of MnO 2 /graphene. This connection allowed the adjacent attack and validated the dual-site mechanism. The L-H d model was consistent with the predicted reaction rate of toluene removal with a correlation coefficient near unity (r 2 = 0.9165). Moreover, the physical criterion was in accordance with both enthalpy and entropy of toluene adsorption constraints. Fulfillment of mathematical and physical criteria indicated the catalytic ozonation of toluene over MnO 2 /graphene can be well described by the L-H d mechanism. This study helps understand the catalytic ozonation of toluene over MnO 2 /graphene in a closely mechanistic view.

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Section: Introductionmentioning

confidence: 99%

Novel mechanistic view of catalytic ozonation of gaseous toluene by dual-site kinetic modelling

Yao

Hui

et al. 2017

Chemical Engineering Journal

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“…A técnica de fluorescência de raios X, Tabela 2, mostrou que a concentração dos óxidos nos materiais SiMn-X é dependente do precursor utilizado e da sua concentração no meio reacional, sendo que, foram obtidos materiais com quantidades de óxido de manganês maiores do que as descritas na literatura [18][19][20] [9]. Entretanto, não podemos descartar a hipótese de que estas espécies também podem se localizar dentro dos poros da matriz de SiO 2 .…”

Section: Resultsunclassified

“…() Sílica Pura; () SiMn-B e () SiMn-E A Figura 3 exibe os difratogramas de raios X para os materiais SiMn-A, SiMn-B e SiMn-B/400, obtidos a partir do precursor de acetato. A presença de um pico largo ao redor de 2θ = 23 0 , halo amorfo típico de sílica vítrea [20], indica que esses materiais são amorfos. No entanto, com o aumento da concentração do precursor de manganês, observa-se o aparecimento de outra banda larga entre 35 0 e 36 0 , de baixa intensidade, que pode indicar a presença do óxido Mn x O y [18][19][20].…”

Section: Figuraunclassified

“…A presença de um pico largo ao redor de 2θ = 23 0 , halo amorfo típico de sílica vítrea [20], indica que esses materiais são amorfos. No entanto, com o aumento da concentração do precursor de manganês, observa-se o aparecimento de outra banda larga entre 35 0 e 36 0 , de baixa intensidade, que pode indicar a presença do óxido Mn x O y [18][19][20]. Para o material SiMn-B/400, que corresponde ao material SiMn-B/400, observou-se o aparecimento de um pico largo ao redor de 2 = 33 0 , que pode ser atribuído ao pico de difração mais intenso, plano (222), da rede do Mn 2 O 3 (JCPDS-ICDD, cartão n o .…”

Section: Figuraunclassified

“…Em função de sua estabilidade química, de seu baixo custo e de ser ambientalmente benigna, a família dos óxidos de manganês tem recebido grande atenção atualmente [9,[11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30], e esses óxidos têm se destacado por suas potenciais aplicações na área de materiais para aplicação em energia, por exemplo, como catalisadores na oxidação da água, em sistemas de fotossíntese artificial [23][24][25][26][27], ou como catalisadores na reação de redução de oxigênio molecular (RRO) em pilhas a combustível alcalinas [27][28][29][30]. Recentemente, vários artigos vêm estudando a atividade catalítica dos óxidos de manganês na reação de redução de oxigênio molecular [11][12][13][14][15][16][17][27][28][29][30].…”

Section: Introductionunclassified

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Síntese de óxidos mistos SiO2 /Mn xOy para aplicação na reação de redução de O2

et al. 2013

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RESUMOOs óxidos mistos SiO 2 /M x O y obtidos pelo processo sol-gel, designados de compósitos, normalmente aliam as propriedades mecânicas e químicas da sílica gel com as propriedades químicas do óxido metálico (M x O y ), apresentando propriedades tais como: elevado grau de dispersão e homogeneidade das partículas do óxido metálico na matriz de sílica, assim como elevada resistência mecânica e química. O objetivo deste trabalho foi o de preparar e caracterizar materiais do sistema SiO 2 /Mn x O y , obtidos pelo processo sol-gel, utilizando diferentes concentrações dos precursores de Mn (II), acetato ou nitrato. A técnica de fluorescência de raios X (FRX) mostrou que a concentração do óxido metálico nos materiais é dependente do precursor utilizado e da sua concentração no meio reacional, variando de 9,4% até 20,9% em massa. A maior concentração de óxido de manganês foi obtida quando se utilizou como precursor o (CH 3 CO 2 ) 2 Mn.4H 2 O. Os espectros de infravermelho indicam que a rede de SiO 2 é pouco perturbada pelo aumento da quantidade de óxido de manganês, sugerindo que o Mn x O y está disperso na superfície da matriz de sílica. Os difratogramas de raiosX (DRX) mostram que os materiais apresentam baixa cristalinidade. No entanto, observa-se uma mudança no DRX em 2θ = 35,7 o quando o material é aquecido a 400 0 C, provavelmente devido à formação de cristalitos de Mn 3 O 4 . O método de síntese proposto para os materiais SiO 2 /Mn x O y é reprodutível. A aplicação destes materiais como eletrodos para a redução de O 2 foi avaliada e observou-se que a atividade eletrocatalítica desses materiais pode ser aumentada através do seu aquecimento a 400 0 C. Palavras-chave:Sol-Gel, óxidos mistos, sílica gel, óxido de manganês, compósito. ABSTRACTThe mixed oxides SiO 2 /M x O y obtained by the sol-gel process, designated as composites, usually combine both mechanical and chemical properties of silica gel with the chemical properties of metal oxide (M x O y ), showing properties such as: high degree of dispersion and homogeneity of metal oxide particles in the silica matrix, as well as high mechanical and chemical resistance. The goal of this work was to prepare and characterize materials in the system SiO 2 /Mn x Oy obtained by the sol-gel process, using different concentrations of Mn (II) precursors (acetate or nitrate). The technique of X-ray fluorescence showed that the concentration of metal oxide in the materials is dependent on the precursor used and its concentration, ranging from 9.4% up to 20.9% by mass. The highest concentration of manganese oxide was obtained when (CH 3 CO 2 ) 2 Mn.4H 2 O was used as precursor. The infrared spectra indicate that the network of SiO 2 is not disturbed by the increase in the quantity of manganese oxide, suggesting that the Mn x O y is dispersed on the surface of the silica matrix. The X-ray diffraction showed the low crystallinity of these materials. However, there is a change in the XRD on 2θ = 35.7 0 when the material is heated to 400 0 C, probably due to the formation of Mn 3...

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Alkali‐Metal‐Promoted Pt/TiO₂ Opens a More Efficient Pathway to Formaldehyde Oxidation at Ambient Temperatures

et al. 2012

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Formaldehyde is emitted from building and furnishing materials and consumer products, [1] and is known to cause irritation of eyes and respiratory tract, headache, pneumonia, and even cancer. [2,3] It is a dominant indoor air pollutant, especially in developing countries, and significant efforts have gone into indoor HCHO purification to meet environmental regulations and human health needs.Removal of HCHO by adsorbents has been investigated extensively using potassium permanganate, activated carbon, aluminum oxide, and some ceramic materials. [4][5][6] Sorbent effectiveness is typically limited by low adsorption capacities. Catalytic oxidation is the most effective technology for volatile organic compound (VOC) abatement because VOCs can be oxidized to CO 2 over certain catalysts at much lower temperatures than in thermal oxidation. [7][8][9] Supported noble metal catalysts (Pt, Pd, Rh, Au, Ag) or metal oxide catalysts (Ni, Cu, Cr, Mn) have been used for the catalytic oxidation of VOCs. [8][9][10][11][12][13][14][15][16][17][18][19][20][21][22] Complete oxidation of HCHO over catalysts occurs above 150 8C on clean and oxidized films of Ni, Pd, and Al [15] and over silver-cerium composite oxide, [16] above 100 8C over Ag/MnOx-CeO 2[18] and Au/CeO 2 , [19] and above 85 8C over Pd-Mn/Al 2 O 3[17] and Au/FeOx. [20] As catalytic oxidation at even lower temperatures is desirable for indoor air purification, the development of a catalyst for total HCHO oxidation at room temperature is of great interest. In our recent study, [21,22] 1 % Pt/TiO 2 catalyst was shown to be effective for HCHO oxidation at room temperature, achieving 100 % conversion of d = 100 ppm HCHO to CO 2 and H 2 O at a gas hourly space velocity (GHSV) of 50 000 h À1 . However, we also observed that this type catalyst is not as active as needed for practical applications, and deactivates with time-on-stream.Herein, we report a novel alkali-metal-promoted Pt/TiO 2 catalyst for the ambient destruction of HCHO. We show that the addition of alkali-metal ions (such as Li + , Na + , and K + ) to Pt/TiO 2 catalyst stabilized an atomically dispersed Pt-O(OH)x-alkali-metal species on the catalyst surface and also opened a new low-temperature reaction pathway, significantly promoting the activity for the HCHO oxidation by activating H 2 O and catalyzing the facile reaction between surface OH and formate species to total oxidation products. Figure 1 a shows the HCHO conversion to CO 2 as a function of temperature over the x % Na-1 % Pt/TiO 2 (x = 0, 1, and 2) samples at a GHSV of 120 000 h À1 and HCHO inlet of d = 600 ppm. All gas streams were humidified to a RH of around 50 %. Before each activity test, the samples were reduced in H 2 at 300 8C for 30 min. The sodium-free catalyst had low activity for the HCHO oxidation reaction, with HCHO conversion being only about 19 % at 15 8C. With 1 % Na addition, the HCHO conversion reached 96 % at 15 8C and 100 % at 40 8C. With 2 % Na addition, 100 % HCHO conversion to CO 2 and H 2 O was measured at 15 8C. The effect of ...

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Structure and Oxidation State of Silica-Supported Manganese Oxide Catalysts and Reactivity for Acetone Oxidation with Ozone

Cited by 111 publications

References 30 publications

Novel mechanistic view of catalytic ozonation of gaseous toluene by dual-site kinetic modelling

Novel mechanistic view of catalytic ozonation of gaseous toluene by dual-site kinetic modelling

Síntese de óxidos mistos SiO2 /Mn xOy para aplicação na reação de redução de O2

Alkali‐Metal‐Promoted Pt/TiO₂ Opens a More Efficient Pathway to Formaldehyde Oxidation at Ambient Temperatures

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Structure and Oxidation State of Silica-Supported Manganese Oxide Catalysts and Reactivity for Acetone Oxidation with Ozone

Cited by 111 publications

References 30 publications

Novel mechanistic view of catalytic ozonation of gaseous toluene by dual-site kinetic modelling

Novel mechanistic view of catalytic ozonation of gaseous toluene by dual-site kinetic modelling

Síntese de óxidos mistos SiO2 /Mn xOy para aplicação na reação de redução de O2

Alkali‐Metal‐Promoted Pt/TiO2 Opens a More Efficient Pathway to Formaldehyde Oxidation at Ambient Temperatures

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Alkali‐Metal‐Promoted Pt/TiO₂ Opens a More Efficient Pathway to Formaldehyde Oxidation at Ambient Temperatures